22 NON-METALLIC SIMPLE SUBSTANCES. PART i. 



through a glass tube filled with any of these three gases, 

 much attenuated, they slowly combine with the platinum 

 wire of the negative pole of the battery inserted in the 

 tube. The electricity by degrees passes in diminished 

 quantity, and at last ceases altogether, showing that 

 matter, however attenuated, is requisite to conduct it. 



According to the experiments of M. Dumas, the 

 volatility of a compound is in the inverse ratio of the 



% condensation of the substances composing it, and simple 

 bodies come under the same law. For example, chlorine 



^is more volatile than bromine, and bromine is more 

 volatile than iodine ; hence according to that law, 

 chlorine is the least dense of the three, bromine is 

 intermediate, and iodine is the most dense, which is 

 actually the case : for chlorine is a gas, bromine a liquid, 

 and iodine a solid at ordinary temperatures, which 

 proves that there is a sequence in the intensity of the 

 cohesive forces in this triad. 



